From Wikipedia:

>The tenth mission for Challenger, STS-51-L, was scheduled to deploy the second in a series of Tracking and Data Relay Satellites (TDRS-B), carry out the first flight of the "Shuttle Pointed Autonomous Research Tool for Astronomy" (SPARTAN-203) / Halley's Comet Experiment Deployable in order to observe Halley's Comet, and carry out several lessons from space as part of the Teacher in Space Project and Shuttle Student Involvement Program (SSIP).